
48 MATHEMATICS
TRY THESE
Is getting an even number an event? Since an even number could be 2, 4 or 6, getting an
even number is also an event. What will be the probability of getting an even number?
It is
Example 3: A bag has 4 red balls and 2 yellow balls. (The balls are identical in all
respects other than colour). A ball is drawn from the bag without looking into the bag.
What is probability of getting a red ball? Is it more or less than getting a yellow ball?
Solution: There are in all (4 + 2 =) 6 outcomes of the event. Getting a red ball
consists of 4 outcomes. (Why?)
Therefore, the probability of getting a red ball is
=
. In the same way the probability
of getting a yellow ball =
(Why?). Therefore, the probability of getting a red ball is
more than that of getting a yellow ball.
Suppose you spin the wheel
1. (i) List the number of outcomes of getting a green sector
and not getting a green sector on this wheel
(Fig 4.8).
(ii) Find the probability of getting a green sector.
(iii) Find the probability of not getting a green sector.
4.3.5 Chance and probability related to real life
We talked about the chance that it rains just on the day when we do not carry a rain coat.
What could you say about the chance in terms of probability? Could it be one in 10
days during a rainy season? The probability that it rains is then
. The probability that it
does not rain =
. (Assuming raining or not raining on a day are equally likely)
The use of probability is made in various cases in real life.
1. To find characteristics of a large group by using a small
part of the group.
For example, during elections ‘an exit poll’ is taken.
This involves asking the people whom they have voted
for, when they come out after voting at the centres
which are chosen off hand and distributed over the
whole area. This gives an idea of chance of winning of
each candidate and predictions are made based on it
accordingly.
← Number of outcomes that make the event
← Total number of outcomes of the experiment.
Fig 4.8